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Ubiquitin is a small protein consisting of 76 amino acids that is important for the regulation of protein function in the cell. Ubiquitylation and deubiquitylation are enzymatically mediated processes by which ubiquitin is covalently bound or cleaved from a target protein. These processes have been implicated in the regulation of many cellular functions including cell cycle progression, apoptosis, modification of cell surface receptors, regulation of DNA transcription and DNA repair. Thus, the ubiquitin system has been implicated in the pathogenesis of numerous disease states including inflammation, viral infection, metabolic dysfunction, CNS disorders, and oncogenesis.
Ubiquitin molecules are cleaved from proteins by deubiquitylating enzymes (DUBs), of which there are approximately 95 DUBs in human cells, divided into sub-families based on sequence homology. The ovarian tumour (OTU) family consists of at least 14 active DUBs and are characterised by the presence of an OTU domain and the tendency to cleave ubiquitin chains in a linkage specific manner. Cezanne 1, also known as OTUD7B, is an 843 amino acid protein that was identified owing to its similarity to the OTU family member A20 that has been shown biochemically to have a strong preference for K11 ubiquitin chain linkages.
Cezanne 1 has been shown to act as a negative regulator of both the canonical and the non-canonical NF-κB pathway. It has been shown that Cezanne 1 acts on the canonical pathway by processing K63 chains on the RIP 1 protein and on the non-canonical pathway by deubiquitylation of the inhibitory component TRAF3 (TNF receptor associated factor 3). It has also been shown to have a role in hypoxia by regulating HIF1α (hypoxia inducible factor 1α) protein levels. Cezanne 1 siRNA decreased HIF1α protein levels under hypoxia, and accordingly decreased HIF1α target gene expression. Knockdown of Cezanne 1 led to higher levels of apoptosis following hypoxia. Since HIF1α has oncogenic properties, and Cezanne 1 has a pro-survival role in hypoxia, Cezanne 1 has been suggested to be a good target for pharmacological intervention.
Cezanne 1 has been shown to have a role in cell proliferation, migration and invasion by antagonizing EGFR (epidermal growth factor receptor) internalisation and degradation. Cezanne 1 and Cezanne 2 were identified in a genetic screen to find a DUB enzyme for EGFR. Cezanne 1 overexpression led to higher levels of phosphorylated EGFR, lower levels of ubiquitylated EGFR and EGFR stabilization. In MDA-MB-231 breast cancer cells, knockdown of Cezanne 1 led to decreased invasion and migration. Analysis of The Cancer Genome Atlas by Pareja et al., showed that Cezanne 1 was overexpressed in breast cancer and amplification of the gene was seen in a third of breast tumours. The level of Cezanne 1 expression correlated with poor prognosis.
Although there has been a handful of DUB inhibitors published in the literature, there is a continuing need for compounds and pharmaceutical compositions which inhibit DUBs such as Cezanne 1 and USP30 for the treatment of cancer and other indications where DUB activity is observed.